In modern digital integrated circuits, particularly those fabricated according to the well-known complementary metal-oxide-semiconductor (CMOS) technology, circuit operation often depends upon the availability of a stable reference voltage. For example, many functional circuits internal to an integrated circuit rely upon current sources that conduct a stable current. Examples of such functional circuits include differential amplifiers, current mirrors, operational amplifiers, level shift circuits, and circuits that themselves generate reference voltages. Since current sources are generally implemented by way of field effect transistors, the stability of the current source depends upon the stability of the reference voltage applied to the gate of the field effect transistor.
In particular applications, however, it is beneficial for the voltage reference circuit to have a relatively low output impedance, so that it can source or sink significant current in a relatively short transient period, without the reference voltage itself modulating as a result of the current draw. As will be apparent from the description hereinbelow, such low output impedance may be obtained in a voltage reference circuit, but requiring significant DC current drawn thereby.
It is therefore an object of the present invention to provide a voltage reference circuit having a low output impedance while achieving low DC current drawn thereby in its use.
It is another object of the present invention to provide such a circuit which can allow for reduction in DC current during portions of the integrated circuit operating cycle.
Other objects and advantages of the present invention will be apparent to those of ordinary skill in the art having reference to the following specification together with its drawings.